Communications and data transmission systems that transmit information signals in the form of optical pulses over optical fiber are now commonplace, and optical fibers have become the physical transport medium of choice in long distance telephone and data communication networks due to their signal transmission capabilities, which greatly exceed those of mechanical conductors. Despite their advantages, however, difficulties in their manufacture must be overcome in order for high-yield, high-quality and error-free optical fiber to be produced in mass. One such manufacturing problem is maintaining the appropriate thickness and concentricity of optical fiber layers.
As shown by the optical fiber cross-section illustrated FIG. 1, the production of optical fiber 10 traditionally utilizes a minimum of two layers of coating 20, 24 covering a glass center 18 having a core 16, as is well known in the art. The two layers of coating 20, 24 comprise an inner, or primary, layer of coating 20, and an outer, or secondary, layer of coating 24. In many circumstances maintaining control of the thickness 21 of the primary layer of coating 20 is of critical importance when considering fiber performance parameters such as microbending loss and modulus. In wet-on-wet coating applications, in which the application of the primary layer of coating 20 is immediately followed by application of the secondary layer of coating 24, which is applied directly over the viscous, still-wet primary layer of coating 20, no technique exists by which to measure the primary outer diameter (POD) 22 of the primary layer of coating 20 online during the drawing of the fiber 10.
Controlling the POD 22 is essential to producing optical fiber to within prescribed limits, thus ensuring acceptable levels of optical fiber performance. Currently, however, controlling the POD 22 assumes that the die geometry, coating viscosity and coated fiber outer diameter are all consistent and known. Any variability in these parameters will cause variability in the POD 22. At present, this variability cannot be measured during the drawing of the optical fiber (also referred to herein as ‘online’), and therefore cannot be corrected until after the fiber is formed.
Therefore, what is needed is a system, method and apparatus to estimate and control optical fiber primary coating diameter in wet-on-wet fiber manufacturing.